Technical Field of Invention
The invention disclosed and taught herein relates generally to a system and method for use of a vehicle for use in environments such as but not limited to subsea environments.
Background of the Invention
Pipeline support and stabilization mattresses have been used in subsea operations. There have been various designs over the years. For example, some of the early designs used large canvas bags that included materials such as bituminous material mixed with aggregates. There were issues with these designs. For example, when these mattresses were left of the deck of a vessel, they were prone to softening and the heat from the engine rooms or exposure of sunlight could affect the shape of the mattresses. Once installed in subsea locations, the mattresses could become brittle, crack, and become stiff enough to not properly lay on the pipeline or spool they were installed over. This could lead to accidents related to moving or lifting the mattresses.
Subsequently, concrete mattresses were introduced. These concrete mattresses were referred to as link-lok mattresses. These mattresses were usually a sheet of premade plastic pots connected together by rope. The plastic pots contained cured concrete. This allowed for easier transportation of the pots to a remote location before the filling and the curing of the concrete in the pots. Unfortunately, this method proved to be expensive. Additionally, it became impractical to revert to the bituminous type mattresses due to new regulations.
Accordingly, a new method was introduced that installed and positioned mold produced concrete mattresses with either installation frame, beam, or speedloader frames. In this configuration, mattresses have to be installed and repositioned individually. This is advantageous because the frame can carry three to five mattresses. Moreover, this method requires a diver and a remotely operable vehicle (“ROV”) to deploy the mattresses.
These methods include recovery by frame or beam. In this method, mattresses are either recovered to the surface one at a time using either the lifting beam or frame wherein the rigging is connected either by divers or ROV intervention. Alternatively, a small number of concrete mattresses are loaded onto speedloaders at the seafloor and then lifted to the surface for re-use or disposal.
Another method is recovery by subsea modified skip or half-height. In this method, the mattresses must be individually rigged by diver or ROV at the seafloor using the frame/beam method described above, then lifted and placed into a modified half height container, which in turn must then be lifted to the surface via surface vessel or platform deck crane.
Another method is recovery by steel wire rope nets or custom flat-racks. This method is a variation/alternative to the speedloader method described above, where by a number of mattresses are loaded subsea one at a time onto either out-spread steel cargo nets or flat-racks using the diver or ROV rigged frame/beam method and then the nets/flat racks are lifted to the surface via the vessel/platform deck crane.
Another method is recovery by hydraulic grapple connected to vessel/platform deck crane. In this method, mattresses are lifted individually by large hydraulic grapple, subsea which partially crushes the mattress structure and the load is recovered to the vessel/platform deck.
There are issues with each of these methods. For example, recovery of mattresses through the splash zone using the integral polypropylene rope loops are not recommended due to concerns regarding the integrity of the loops prior to attempting the lift.
Similarly any method which relies on the interaction of divers to complete the mattress lifting or positioning activity, including guiding and orientating the suspended mattresses in the half heights subsea, may be considered as a high risk activity.
Moreover, when subsea half heights/containers are used, the total lift loads may be difficult to establish and there also may be high seabed suction loads. The method is also difficult for high volumes of mattress recovery because of the number of containers required and the amount of space required on the vessel deck.
Furthermore, the use of the grapple to lift mattresses may be dangerous to personnel on the vessel deck as the load in recovered and there is a chance of snagging the underlying umbilical or pipeline as the mattress is grabbed and lifted from the seabed.
Therefore, a need exists to develop a recovery vehicle the can provide improvements over these systems when used.